Do you have any examples?
https://www.fiestastforum.com/
https://www.mustang6g.com/forums/
Almost every new generation of car will either get a new forum website, or added forum group. Fun fact, a lot of these are owned by one company. There is also tapatalk which charges money for access.
https://www.mustang6g.com/forums/
https://www.camaro6.com/forums/
Most car related subreddits are used like instagram or news aggregators with very little substance you can't easily find elsewhere.